1. Field of the Invention
The present invention relates to a recording and reproducing apparatus and, more particularly, to a recording and reproducing apparatus which is suitable for use in a rotary head type video tape recorder.
2. Description of the Prior Art
In general, a gain of a reproducing amplifier is set to only a single value or to a plurality of special values corresponding to modes such as a normal reproducing mode, a variable speed reproducing mode, and the like. An AGC circuit is made operative for an excessive input signal.
In the above conventional technique, for instance, in the case where RF signals of envelope waveforms WEN of different envelope levels are obtained from A and B channels, respectively, as shown in FIG. 1A, when levels of the RF signals are detected, a gain control is executed without distinguishing the A and B channels, so that there is a problem such that it is difficult to finely adjust the level. Therefore, there are problems such that a circuit to cope with variations in dynamic range and input level needs to be provided for a video signal processing circuit at the post stage. The above problem becomes a cause of deterioration in characteristics.
According to the conventional technique using the AGC circuit, the gain control is performed for the continuous RF signals which are derived from both of the A and B channels as shown in FIG. 1A, so that there are problems such that a reaction is delayed due to a time constant of the response and waveforms like mustaches appear as shown by arrows X in FIG. 1B at change points (i.e., switching time points of the channels in the example shown in the diagram) t.sub.BA and t.sub.AB.
The envelope levels of the reproduction RF signals for a recording current depend on a length (hereinafter, referred to as a depth) D of a tip portion of a magnetic head 35 shown in FIG. 2. When the magnetic head 35 is abraded and the depth D decreases due to the use of the video tape recorder for a long time, a reproducing sensitivity of the magnetic head 35 is improved, so that the envelope levels of the RF signals also increase. In FIG. 2, reference numeral 36 denotes a coil and reference numerals 37 and 38 indicate terminals to supply a recording current, respectively.
There are problems such that it is difficult to correct such a time-dependent change of the magnetic head by the conventional techniques and such a time-dependent change becomes a cause of the deterioration in characteristics of the video signal.
Further, there are problems such that the conventional adjusting works are complicated and require the experienced operations and also need a large number of adjusting steps.